Gas cylinder actuators in general are formed by a tubular jacket for gas containment that is sealed hermetically at one end by a bottom provided with a gas filling valve, and at the opposite end by a head portion, which is provided with a hole for the passage of a stem with a piston, which performs a translational motion inside the jacket; the jacket, the bottom and the head portion form the stroke chamber for the piston, while the piston itself, with the jacket and the bottom, forms the gas compression and expansion chamber.
Such gas cylinder actuators are used typically, but not exclusively, also in situations, such as molds, molding presses and the like, in which they can be subjected to such operational conditions that they might be damaged; such damage can render the gas cylinder actuator itself unusable, with the need to replace it and interrupt the work of the machine or plant in which it is arranged to work, but it can also injure an operator who is in the vicinity, as in the case of an explosion caused by overpressure, or in the case of ejection of the stem due to breaking of the piston, caused by an unexpected and uncontrolled rising thrust caused by the pressurized gas.
Experience shows that the most critical condition is observed in the case in which a mold, on which a gas cylinder actuator operates, jams with the actuators in the compression configuration, and then the same mold is suddenly released, causing an unexpected return thrust of the piston stem, such as to break, as a consequence of an impact, either the head portion that retains the piston stem in the jacket or the piston stem.
In both cases, there is the great risk that the stem might be ejected with force, with great danger to any personnel that may be in the vicinity.
In order to obviate this drawback various means and devices for avoiding the uncontrolled ejection of the stem are currently known.
A first type of such devices is provided with an auxiliary safety shoulder, formed on the stem proximately to the piston, so that if there is a fracture between the piston and the stem in the junction region, the stem is retained inside the jacket thanks to the abutment of its auxiliary shoulder against a corresponding extraction-preventing shoulder provided on the head portion of the gas cylinder actuator.
In a second type of safety device for preventing the ejection of the stem, a predetermined part of the piston or of the stem is separated as a consequence of an impact of predefined strength, and this part damages the sealing gasket of the piston or of the stem, allowing the external discharge of the pressurized gas and preventing the violent and uncontrolled ejection of the stem.
Both of these types work to retain the stem inside the jacket.
Events could occur, however, for which the predefined breakages in the types mentioned above are not sufficient to ensure a discharge of the pressurized gas that is fast enough to prevent the gas cylinder actuator from yielding in other points in addition to the ones provided, or to prevent the piston stem from being ejected.